1. Field of the Invention
This invention relates to an improvement in or relating to an apparatus adapted to remove water droplets stuck on the surface of a silicon wafer, glass photomask or the like by a centrifugal force and to dry same.
2. Description of the Prior Art
The above apparatus is used, after washing a silicon wafer or the like with water, to remove water and to dry the silicon wafer of the like. It is constructed of a rotor to be driven and a generally cylindrical casing which embraces the rotor. The rotor is provided with one or more holders each adapted to hold a cage-shaped carrier which is used to enclose an item to be treated (e.g., a wafer), namely a carrier holder. On the other hand, a lid centrally defining an air intake port is provided over the casing while an exhaust port is formed in the circumferential wall of the casing at a suitable location thereof. When the rotor is driven, water droplets present on the surface of a wafer or the like are thrown off in an air stream by virtue of centrifugal forces applied thereto toward the circumferential wall of the casing and are then collected on the bottom wall of the casing. Since a negative pressure is developed at this time in a central region of the rotor, air is drawn into the rotor through the air intake port and is then caused to flow in a circumferential direction through the casing, and is eventually discharged through the exhaust port. The wafer or the like is thus dried up by the air stream.
Accordingly, besides water droplets, dusts and stains are also caused to stick on the circumferential wall of the casing and are then allowed to drip down, thereby causing such dusts and stains to accumulate on the bottom wall of the casing. In an apparatus of the above type, the air in the casing does not flow in its entirety in the circumferential direction but a part of the air may flow in the radial direction and/or may swirl upwardly. In some instances, air streams which flow in the radial direction or swirl upwardly strike against the circumferential wall and against the bottom wall and flow backward, thereby carrying water, dusts and stains on the circumferential wall and on the bottom wall back onto the wafer or the like. Such a prior art apparatus is thus accompanied by drawbacks that such radial air flows and/or upward air swirls lower the drying efficiency and affect adversely on the effectiveness of the washing treatment.